1. Technical Field
This invention pertains to apparatus for monitoring respiration and more particularly to apparatus of this type which employ conductors disposed about the torso of a subject for expansion and contraction therewith as the subject breathes.
2. Prior Art
Commonly assigned U.S. Pat. No. 4,308,872 entitled METHOD AND APPARATUS FOR MONITORING RESPIRATION, the contents of which are incorporated herein by reference, discloses a particular respiration monitoring apparatus. The apparatus disclosed in the patent employs two electrical conductors, e.g. wires, one disposed in encircling relation about the chest and the other disposed in encircling relation about the abdomen. Each conductor comprises the inductance element of an LC oscillator circuit of fixed capacitance. Consequently, the frequency of each oscillator varies solely in response to changes in the inductance of its respective conductor which, in turn, varies in response to changes in the volume encircled by the conductor. Therefore, as the subject breathes, the frequency changes at the outputs of the oscillators continuously indicate the extent of the expansion and contraction of the subject's chest and abdomen. As more fully explained in said U.S. Pat. No. 4,308,872, by properly processing these signals, significant respiration data may be obtained.
For the aforementioned apparatus to function properly, it is important that the conductors fit snugly about the subject's torso such that the expansions and contractions of the conductors closely follow the expansions and contractions of the chest and abdomen. Further, since it is impractical to render the conductors expandable, some other mechanism for accommodating expansion and contraction of the conductors must be employed.
In accordance with a structure now in use by applicants, each conductor is supported on a strip of woven fabric securable about the subject's torso. The fabric strip or band is stitched under tension by a plurality of longitudinally extending elastic stitches in a process known as shirring. Consequently, when the tension is released, the fabric becomes bunched or puckered along its entire length. Thereafter, an insulated wire conductor is stitched to one side of the fabric in a zigzag or saw tooth pattern. In this construction, stretching of the fabric in a longitudinal direction is accommodated by the puckers or folds with corresponding extension of the wire being accommodated by a widening and flattening of the saw tooth pattern. Consequently, by selecting the length of the band in its unstretched condition to be less than the circumference of the torso portion to be encircled, the band may be stretched about the torso portion for a snug fit. In the band structure now being described, the ends of the band are secured together as by a hook and loop type fastener, such as Velcro.TM., complementary portions of which are secured by stitching to either end of the band.
To accommodate connection of the wire to the balance of the oscillator circuit, the wire is secured to the fabric such that both ends of the wire terminate at the same longitudinal edge of the band at either end thereof, whereby when the band is secured about the torso, the ends of the wire are next to each other. The ends of the wire are stripped and soldered to connecting pins which are then secured in shrink tubing such that the tips of the connecting pins are exposed. The shrink tubing is stapled to the ends of the band.
The balance of the oscillator circuit is secured in a housing which, in use, may be taped to the band for the sake of convenience. A cable extending from the housing has female connectors which releasably mate with the connecting pins on the wire for completing the oscillator circuit. A second cable extends from the housing for inputting the variable output of the oscillator to additional processing circuitry as more fully described in said U.S. Pat. No. 4,308,872.
While the foregoing construction serves its intended function, it suffers from several drawbacks. One drawback is that the construction of the band is not suitable for mass production thereby adding significantly to the cost of each band. For example, the required multiple stitching operations are time consuming as is the soldering of the pins to the ends of the wire. A further drawback resides in the press fit connectors which releasably join the wire conductor to the cable extending from the oscillator housing. These connectors may become loosened due, for example, to undesirable movements of the subject, as is common in neonatal applications. A loose connector can create noise sufficient to significantly impair the quality of the transmitted signal. Even worse, the connectors may disconnect altogether. Then too, because of the low noise requirement, low noise, high cost connectors must be employed which further add to the overall cost of the band.
Another drawback, related to the first, is that owing to the high cost of the bands, it is impractical to discard them after a single use. Yet in the medical field, where sanitary considerations are paramount for sound medical reasons as well as psychological ones, it is preferred to render disposable any apparatus that comes into contact with the patient, such as occurs with the band.
Yet a further drawback is that due to the particular structure of the bands, they are not suited to cleaning by machine, as there is a risk of damaging the pins or severing the stitching securing the wire in place. Then too, the hook and loop type fastener which secures the ends of the band in encircling relation about the torso is also not suited to machine washing as it can become entangled in the fabric.
It is accordingly an object of the present invention to provide a band which overcomes the aforementioned drawbacks.
It is a further object of the present invention to provide a band which can be constructed at a sufficiently minimal cost that the band can be discarded after a single use.
It is yet a further object of the invention to provide a band which can be mass produced.
It is still a further object of the present invention to provide a band in combination with an improved housing for the oscillator circuit wherein the wire is joined to the circuitry within the housing in a manner that significantly reduces, if not eliminates, the possibility of the wire becoming loose or disconnected.
It is also an object of the invention to provide a band which does not require high cost connectors for joining the wire to the circuitry within the housing.
It is-also an object of the invention to provide a method of making a band which meets the stated objectives.